As an example of a control system application, many modern cars use a four-stroke combustion cycle to convert gasoline into motion. FIG. 1 illustrates the four strokes of a four-stroke engine, namely: intake stroke 10, compression stroke 12, combustion stroke 14, and exhaust stroke 16. FIG. 1 also illustrates aspects of an engine that is capable of implementing the four-stroke cycle. These illustrated aspects include a piston 18 that is connected to a crankshaft 20 by a connecting rod 22.
In implementing the four-stroke cycle, the piston 18 may move within a cylinder 24 as follows: During the intake stroke 10, the piston 18 starts at the top of the cylinder 24, an intake valve opens, and the piston 18 moves downward to let the engine take in a cylinder-full of air and fuel. Typical intake strokes 10 mix a small quantity of gasoline with air, thereby creating a fuel/air mixture. For the intake stroke 10 to work effectively, the intake valve should open at a particular point during the intake stroke 10.
During the compression stroke 12, the intake valve closes and the piston 18 moves upward to compress the fuel/air mixture. The compression stroke 12 makes an explosion during the ensuing combustion stroke 14 more powerful.
During the combustion stroke 14, the piston 18 reaches the top of its stroke, and a spark plug emits a spark to ignite the fuel/air mixture. The fuel/air mixture in the cylinder 24 explodes and drives the piston 18 down. In order for the combustion stroke 14 to work effectively, the spark plug should emit the spark at a particular point during the combustion stroke 14.
Lastly, during the exhaust stroke 16, the piston 18 hits approximately the bottom of the cylinder 24, an exhaust valve opens, and the piston 18 moves upward. In moving upward, the piston 18 pushes the exhaust out of the cylinder 24 and the exhaust exits through the exhaust system. At this point, the engine is ready for the next cycle, so it begins another intake stroke 10. In order for the exhaust stroke 16 to work effectively, the exhaust valve should open at a particular point during the exhaust stroke 16.
Thus, as one can see, the four-stroke cycle can be characterized by a piston 18 that moves in a linear fashion. As noted above, various events (e.g., an intake valve opening or closing, a spark plug emitting a spark, an exhaust valve opening or closing) should occur at particular points in time in the four-stroke cycle. In short, each piston 18 of an engine drives the rotational motion of the crankshaft 20, which in turn provides power to drive a vehicle. Thus, to provide for adequate operating efficiency, a four-stoke engine would benefit from a control system that accurately monitors and/or controls aspects of an operating engine.
In like fashions, control systems in other applications should adequately monitor and/or control various aspects of the apparatus or process being controlled.